Modulating and amplifying system



l Feb. 3, 1948,. M NlKls 2,435,547

MODULATING AND AMPLIFUNG $YSTEM Filed Apri124, 1959 Manu/.Arma

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Flgnz I 9 9 n 2m m lz/ u Mw L wg?? Mr i Low FefuEA/cr souzcf Low refpuf/vcy .soz/eef Patented Feb. 3, 1948 UNITED ofV :improving the v efciency of radictelephony transmitters.

--ItL-is-.known that inthe modulating tubes or- -in .the itunes amplityne the l modulated fhigh .f-re- ,guency,. the voltage correspondingtotheamplitude o f the .non modulated high frequencyfon-ly @warms Qnqha'lf' Of fthe jlnaximllm Voltage giquev Spondingwtothe Saturation limtofY the tubes-.the

flatter :beina attained only -on inodulationpea-ks. :Owing t thisspare'powerzwhichitisinecessaryrto ferovdefificrinordcr'to permitirle .correct'ftransfr nssionfgof .the :modulation peaks, it follows r that .duringrnost of the time, thatube opelatesionly under half iloadonditions, 'corresponding tov a 4eomparatively .lowfefciency of 1 the order.v ofgf30 while y on .modulation fpeaks, for a .modulation of 100%, theiemciency` ist, substantially twiceggasgreat.

`The modulating or amplifying device vaccorciing to the present invention has the object to remedy this' drawback and is characterised by the fact that it comprisestwo tubes, one of which is saturated by the non modulated amplitude of the carrier; while thefsecond tubeeprov-ides ;theaddi tional power necessary for the-:modulation peaks.

It will be .understood that under `these conditions the "first tube, whichis saturated by the nonflmodulated amplitude off-the vcarrier,"-wiileopf crate constantly with its maximum efficiency, while the second ftube, operating `intermittently at the moments corresponding to the modulation peaks,-will also work undervfull voltage during: its

operating periods, so that the eiilciency of :the entire arrangement will be a maximum.

By way of example there has been described below and represented on the annexed drawing embodiments of the invention.

Figure 1 is a wiring diagram 1n which the device according to the invention is used as a modu` lated HF ampliiier, y Figures '2 to 6 are the current curves illustrating the operation of the device, and

Figures 'I and 8 are diagrams of two alternative embodiments in which the device according to the invention is used as a modulator. 1

The device of Fig. 1 shows diagrammatically a radiotelephony transmitter comprising a genferator I of a high frequency carrier wave, a source 2 providing the low frequency voltage, and a modulator 3 in which the high and low frequencies are combined for supplying the modulated carrier into the output winding 4. The amplifier accord- 2..Claims. (Cl. 179-1715) ing to the'. @invention includes z two tubes 5 f and .i5 preferably connected in @push-pull, .with'f-their grids connectedtoithelterrninals ofthe winding 14. The l.amplifyingtubel 5 :receives throughl vthe conductor 1 a normal biasing voltage; and theplate voltage .applied-to athe" tube'is determined ini-such a manner that the tube will be' saturated* when its grid is supplied with the non modulated carrier. In order "that-the modulation peaks be amplified by the secondtube 6, its grid is given by the conductor 8 to a high negative bias by the Isource `2 0f determined in ai manner that this" tube willonly' start u'-vvoking '-after the modulated Vhigh frequency#voltagehas attained' the"V value corresult thesturationof this tube, it-will' be seen that-finallythe-hlldws2li) i-n the modulation are reproduced, while thernodulation peaks H shown linfdottefd'fllnes, arelglinii'nated. `Figure `'4 -shows the Y"moi'lulateglhigh Z"frequency current supplied Aby the secondtube which -fwill only pass, ifofr the'lreasonsiindicated above, during modulation pea-ks, fvrhilefFigjeshows 'the resulting current inthe-common{output-,circuit 9 of* both tubes. Owing-fte the different Avalues 'of the bias? of'both tubesthe" latter-willl generally not repro duce-identically the parts of the modulation curves corresponding to the modulation hollows and peaks respectlvely, so that the curve of the modulated current will present, as shown in Fig. 5, angular parts such as l2, I2', l2", etc. Means are thus provided to bring the operating point of the second tube, 5, automatically back, during the operating periods of this tube, to a region in the neighbourhood of that of tube 5, so as to ensure a perfect junction of the curves representing the currents of either tube, as shown in Fig. 6. This result may be obtained by means of an auxiliary bias applied to the tube 6 during modulation peaks, for instance, as represented in Fig. 1, by applying to the grid of this tube, through the means of a potentiometer I3, a voltage proportional to the low frequency modulation voltage tapped off on the modulation device 2. An adjust- 66 ment of the potentiometer I3 will offset the operating point of tube 6 for obtaining the required reproduction curve for the modulation peaks. This auxiliary bias may, of course, also be obtained in anyother suitable manner.

The junction f the curve oi' the current supplied by the tube amplifying the peaks with the curve of the current supplied by the tube which is saturated by the carrier may also be obtained without resorting to the use of a variable bias of the former tube, of the type described below.

It will merely be necessary to provide fixed, but

different voltages to either grid and either plate of the tubes and to adjust these voltages in such a manner that the peak tube will commence supplying current at the precise moment when the other tube begins to be saturated. Such an adjustment merely requires that a certain relation be observed between the xed voltages of the electrodes. If: n is the ratio of the load resistance to the internal resistance of the tubes, k the amplification factor of the tubes,

E2 the constant part of the control voltage of the peak tubes, and U1 the constant negative this relation is:

bias of the iirst tube,

I-I-k Mgmt) age, thereby permitting to provide for a modulation of 100%, It may be proved that if this condition, as well as the preceding condition, are satisfied, the reproduction of thermodulated wave by the device is absolutely linear andY free from distortion; the eiliciency on the carrier may attain 70% for a suitable choice of the ratio n of the load resistance to the internal resistance of the tubes.

In the arrangement of Fig. 7, the two tubes 5 and 6 of the device according to the invention are used as modulators, the carrier Wave produced by the generator I and the low frequency from the source 2 being both applied to the control grids I4 and I5 of these tubes. -In the alternative arrangement .of Fig. 8 the two modulating tubes 5 and 6 are pentodes, the control grids I4 and I5 of which receive the high frequency while the low frequency is applied to the suppressor grids I6, I1. In these two arrangements, the auxiliary biasing device of tube 6 has not been shown, which may be realised in any of the manners indicated above.

`What I claim is:

l. Apparatus for modulating a high frequency carrier oscillation and for amplifying the modulated high frequency carrier oscillation comprising, a high frequency carrier source, a modulation voltage source, two thermionic tubes, means for applying the carrier frequency and the modulating voltage to said tubes, means for biasing one of said tubes for operation only at oscillation amplitudes not exceeding the unmodulated carrier level, means for biasing the other of said tubes for operation only at oscillation amplitudes exceeding the unmodulated carrier. level, and means for applying an auxiliary variable biasing voltage to the second tube'for varying the operating point thereof whereby the response characteristic of the two tubes are rendered coextensive.

2. Apparatus for modulating a high frequency carrier oscillation and for amplifying the modulated high frequency carrier oscillation comprising, a high frequency carrier source, a modulation voltage source, two thermlonic tubes, means for applying the carrier frequency and the modulating voltage to said tubes, means for biasing one of'said tubes for operation only at oscillation amplitudes not exceeding the unmodulated carrier level, means for biasing the other of said tubes for operation only at oscillation amplitudes exceeding the unmodulated carrier level, means for applying an auxiliary variable biasing voltage depending on the frequency of the modulating voltage to the second tube for varying the operating point thereof whereby the response characteristic of the tubes are rendered coextensive. i

MARIO NIKIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

